1. Field of the Invention
This invention relates to improvements in a light-intercepting device in a camera having light-intercepting vanes required to be operated (moved) at high speed, like a shutter device such as focal plane shutter or lens shutter or a diaphragm device of a lens.
2. Description of the Prior Art
A shutter device has its light-intercepting vanes required to be moved at high speed for the purpose of securing uniformity of exposure time in various parts of the picture-taking plane, and a diaphragm device has its light-intercepting vanes required to be moved at high speed for the purpose of shortening the stop-down time existing in the exposure operation sequence of a camera. It is conventional to make the light-intercepting vanes themselves lighter in weight for the purpose of high speed movement (as another means, it would occur to mind to increase the driving force of the light-intercepting vanes, but this is not preferable because it increases the load of the film advance lever of the camera or the preset aperture ring of the lens and gives an unpleasant feeling to the operator or, when a motor drive device is mounted on the camera, it increases the power consumption of the motor).
Now, in focal plane shutter devices of the type in which a forward shutter curtain (a first light-intercepting member) and a rearward shutter curtain (a second light-intercepting member) are wound on a drive drum, as is generally called the Leika type, it is known to form the forward and rearward shutter curtains of titanium foil. As the reasons why titanium foil is suited for the drum type focal plane shutter device, mention may be made of (1) its light weight and (2) its low rigidity (the readiness with which it is wound on the drive drum). However, heretofore, none of the diaphragm devices or even shutter devices, particularly, metal blade type focal plane shutter devices in which, as is called the square type, a first and a second light-intercepting member are constituted by vanes of metal (usually carbon steel) and these metal vanes are driven by a link mechanism so as to be parallel-moved just in front of the focal plane to thereby open and close an aperture, has not used titanium material, namely, titanium or titanium alloy for the metal vanes. The reason is as follows:
(a) Titanium material has a relatively low longitudinal elastic modulus (Young's modulus) and thus is lower in rigidity than carbon steel vanes. Therefore, vanes of titanium material are small in deformation resistance and are liable to be deformed during operation and deviated from the movement orbit of the vanes, thus being damaged. That is, to make the most of the above-described advantage of light weight of titanium material in the light-intercepting vanes of the metal blade type focal plane shutters or the diaphragm devices, the low rigidity of titanium material which is advantageous to the drum type focal plane shutter devices has fatal drawback.
(b) In a light-intercepting device constructed by combining a plurality of light-intercepting vanes, the vanes of titanium material, as compared with carbon steel vanes, has disadvantages that sticking is liable to occur and that wear is liable to take place and therefore, not only it is difficult to move the vanes smoothly at high speed but also the connection of the vanes to the link mechanism lacks durability.